1. Field of the Invention
The present invention relates to a method of controlling aircraft, missile, munition or automobiles with plasma actuators, and more particularly to controlling fluid flow across their surfaces, or other surfaces that would benefit from such a method. The present invention is also a method of designing an aerodynamic surface by introducing geometric features which when used in conjunction with a plasma actuator improve the performance of the surface and enable the use of a plasma actuator for aerodynamic and flight control.
2. Technical Background
Traditionally aircraft, missiles, munitions or automobiles use some type of control surfaces to control aerodynamic stability and/or maneuverability during operation. For example, high-lift systems play an important role in the design of aircraft. The wings on most modern-day aircraft are equipped with high-lift systems that are generally in the form of moveable leading-edge slats and trailing-edge flaps. These devices have been shown to enhance the aerodynamic performance of air vehicles through improvements in the coefficient of lift, lift to drag ratio, and stall-angle. Advantages of such “performance-enhancing” devices include improvements in maneuverability, turn rates, glide range and payload, and reductions in takeoff/landing distances and field length requirements. Other traditional control surfaces in the aerospace application include ailerons, rudders, elevators and elerons. Similarly, examples of traditional control surfaces for missiles/munitions include canards, fins and other body extensions, and for automobiles, front and rear spoilers, inlets, and other body extensions.
While the benefits of these conventional control surfaces are well documented, it is also known that the use of moveable control surfaces increase airframe noise and vibration, particularly at high deflection angles. With these types of surfaces, most of the noise originates from the separated flow in the gap or hinge regions, which contribute to the drag component of the viscous or pressure drag on the control surface. At off-design conditions, the drag penalty from these traditional control surfaces is very high. For example, by some estimates used in wing and tail design, eliminating the hinge gaps would result in a 10% drag decrease. In addition, for military applications, the hinge gap is a source of radar wave reflection resulting in a more detectable radar image. Another significant drawback with traditional moving control surfaces is that motors or pneumatics are required for their operation, which adds volume, weight, and cost to aircraft using these types of systems.
In a relentless pursuit to reduce aerodynamic drag, aircraft designers are continuously researching technologies that aim to optimize airfoil shapes to obtain the lowest possible drag during cruise. In 1970s, NASA developed the Natural Laminar Flow (NLF) airfoil series based on computer optimization techniques which improved lift-to-drag (L/D) ratio of airfoils by maintaining laminar flow up to 50% chord. A general feature of NLF airfoils is that the surface pressures remain nearly constant over a significant portion of the airfoil surface, and the profile of the aft pressure recovery region generally attempts to assume a shape that keeps the boundary layer on the verge of separation (zero-wall-shear). Also, in the late 60s and early 70s, the USAF developed a program called “Controlled Configured Vehicles” (CCV) that focused on integrating aerodynamic control surfaces, flow sensors, and automatic control for flight performance and control improvements. This program was successful in showing how this technology could be used to control wing loading during encounters with turbulence, expanding the flutter boundaries, reducing wing weight, and benefits of reduced static stability. This program played a significant role in the designs of present USAF aircraft. The proposed program seeks to achieve similar revolutionary changes in the design of future aircraft surfaces by incorporating advanced flow control technology with conventional and morphing wings.
Adaptive surfaces have been employed on aircraft for effectively changing the leading- and trailing-edge cambers in flight. This has been shown to eliminate sudden pressure jumps due to discontinuous surfaces such as slats and flaps on the wing. Recently, it was shown that the variable camber trailing edge can prevent roll reversal from occurring at flight speeds where the traditional ailerons are no longer effective. While morphing technology has shown the potential to greatly increase the capability of aerodynamic systems. Adapting the wing shape in flight by changing its camber, span, area, sweep angle or twist, would enable an aircraft to radically expanding its flight envelope.
The USAF-Mission Adaptive Wing program demonstrated the advantages of the morphing camber concept. However, one of the major challenges faced by researchers designing a morphing vehicle is the integration of the morphing mechanism into the wing structure along with the use of efficient actuation devices. It is desired to enhance the extent of flow control over an adaptive wing while relaxing some of the power and magnitude requirements for wing articulation.
In view of the foregoing disadvantages of the presently available and conventional moving control surfaces, it is desirable to formalize a method for optimally shaping flow control surfaces for missiles, aircraft, munitions and automobiles, for use with flow control actuators without compromising baseline aerodynamic performance. In addition, it intends to formalize a method for optimally placing flow control actuators, especially plasma actuators on such shapes to maximize a metric of merit such as lift control or reduced drag.